Specialty oils are valuable commodities for a number of reasons, including but not limited to their nutritional, cosmetic, and therapeutic uses. The term “specialty oil” typically refers to oil that occurs in low volume, as compared to commodity oils, has unique functionality or improved health benefits. Many of these specialty oils have anti-bacterial properties and, therefore, can be used to treat infections. Skin care preparations have used oils in formulations for centuries. Additionally, specialty oils have significant health benefits. They can treat a number of serious medical conditions such as diabetes, high blood pressure and cholesterol, migraine headaches, and even certain types of cancer. Specialty oils are able to preserve cell membrane function due to their high content of essential fatty acids and are also rich in antioxidants.
There are a number of oils that fit into the category of specialty oils, many of which are quite expensive. Some oils representatively used in the present invention include, but are not limited to, the following: borage, evening primrose, flaxseed, hemp, black currant, walnut, jojoba, and rosehip seed. It will be apparent to those skilled in the art that other oils may be used with this invention. These oils are a natural source of essential fatty acids that cannot be synthesized by the body (animal or human). Therefore, they must be obtained through proper diet. Deficiency of essential fatty acids has been identified in mental disorders, diabetes, atherosclerosis, hypertension, immune dysfunction, and inflammatory conditions. Each of these oils has specific applications and benefits. For example, borage oil, one of the most expensive oils, helps to repair sun damaged and aging skin, as well as maintain healthy skin. Hemp oil can be absorbed directly into the skin. Jojoba oil is often used in hair care products and applications.
Another specialty oil of great value is sesame oil. Sesame is cultivated in India, China, Sudan, Korea, and Mexico. The oil, which is rich in antioxidants and pain relieving compounds and high in polyunsaturated fat, has natural antibacterial, antiviral, and anti-inflammatory properties. In fact, it has been used in the treatment of conditions such as diabetes, hepatitis, and migraine headaches. Studies have also shown that sesame oil has inhibited the growth of malignant melanoma and the replication of human colon cancer cells due to the fact that it is a cell growth regulator and, therefore, can slow down replication and cell growth. Other research has shown a variety of benefits from the use of sesame oil such as reduction of the bacteria that causes gingivitis, cure of chronic sinusitis, protection from UV rays, and maintenance of beautiful skin. Therefore, because of its human health benefits, as well as the fact that it is a low volume product, sesame oil is considered to be a specialty oil.
Sesame seeds are comprised of approximately 50% to 60% fatty oil containing compounds such as sesamin, sesamolin, and sesaminol. Sesaminol is present in the seeds mainly as glycoside, and it can be produced from sesamolin. More than 75% of sesame oil consists of unsaturated fatty acids, with almost equal portions of oleic and linoleic acid.
In most Asian countries, hot-pressed sesame oil is preferred. The sesame seeds are toasted before pressing. Toasting the seeds increases their flavor, which is a result of the compounds 2-furylmethanthiol, 2-methoxyphenol (guajacol), phenylethanthiol, and 4-hydroxy-2,5-dimethyl-3(2H)furanone (furaneol). Also adding to the flavor are vinylguacol, 2-pentylpyridine, and other N-containing heterocycles.
Specialty oils are obtained from seeds either by mechanical pressing or by extraction. Extraction tends to be a chemical treatment via an organic solvent, such as hexane or a supercritical fluid, such as carbon dioxide.
In the case of specialty oils, mechanical pressing is the preferable route. This is because there is no residual organic solvent left in the cake. There is no evaporation required in either the oil or in the cake. Therefore, these products are very attractive to the organic market. However, mechanical pressing leaves residual oil in the cake. The amount of residual oil depends mainly of the type of expeller and the temperatures used. Additionally, the cake is wasted or used in applications such as feed for livestock for a very low price. The fact remains that each time this process is performed, a significant portion of the specialty oil is not recovered. Because specialty oils are such valuable commodities, the recovery of the oil in the cake would have great economic implications.
An expeller press uses friction and continuous pressure from a screw drive to move and compress the seed material. The oil seeds pass through small openings that do not allow seed fiber solids to pass through. Afterward, the pressed seeds are formed in the press into a hardened cake, which is generally regarded as waste. The residual oil content in the cake depends mainly of the type of the expeller and the temperatures used (cold or hot pressing). The residual oil content in the cake ranges anywhere from 5 to 10 weight percent (wt. %). However, in some cases, such as sesame seeds, the residual oil content can be as high as 20%. At present, the issue of recovering the residual oil from these cakes has not been readily addressed. Historically, the cake is usually discarded or given to livestock for feed.